As a rheumatologist, I am interested in understanding the etiology of extra-intestinal manifestations of inflammatory bowel disease (IBD). Treatment of patients with extra-intestinal IBD is difficult due to few therapeutic options. My ultimate career goal is to understand the mechanism by which extra-intestinal manifestations arise so that targeted therapies may be developed. In this proposal I hypothesize that resident bacteria educate the colonic intraepithelial lymphocyte (IEL) population, which in turn, influences downstream epithelial and immune functions that result in disease. We chose to focus upon colonic IELs in this proposal so that we can begin to link microbiome studies in human populations that are based on colonic samples to downstream mucosal and immune functions. In order to complete these studies and accomplish my ultimate goal of translating my basic research into clinical applications, I require additional career training that includes in vitro modeling, molecular biology, bioinformatics, and translational science. In Aim 1, we will define the role of commensal bacteria in developing the colonic IEL repertoire. Our preliminary data in mice demonstrate that activated, IL-6+ IELs reside in the colon during homeostasis but are depleted when mice are placed on broad- spectrum antibiotics. For this aim, first I will learn microbiome sequencing and analysis through courses in bioinformatics and my mentorship team. Second, we will utilize ovalbumin-specific T cell receptor transgenic mice that will be given oral ovalbumin to determine if T cell antigen recognition alone is sufficient to establish th colonic IEL population. Third, we will utilize conditional gene deletions of MyD88 in IELs and epithelial cells to better understand innate signals that lead to IEL recruitment into the colonic epithelium. Aim 2 will identify the mechanisms by which IEL secreted IL-6 contributes to barrier function through the use of IL-6-/- mice and in vitro model epithelia. I will learn epithelial biolgy in these experiments from my primary mentor Sean Colgan, PhD who has vast expertise in this field. Finally, Aim 3 will focus on the role of trafficking IELs. We will utilize a novel transgeni mouse wherein colonoscopy-induced green-to-red fluorescence is converted, labeling IELs in the distal colon. Again, Dr. Colgan's knowledge of molecular and cellular biology will guide these experiments. In combination with antibiotic-induced dysbiosis, IL-6 deficiency, and a spontaneous model of colitis, we will be strongly positioned to dissect the impacts of resident intestinal bacteria, IL-6, and inflammation on extra- intestinal IEL trafficking. By understanding the development and function of IELs in health and disease, we hope to identify a target pathway for treatment of extra-intestinal IBD. The project described in this proposal in addition to the career development activities will allow me translate our findings into clinical studies correlating microbiome data, IELs, and disease status in patients with IBD and extra-intestinal IBD. Such translational studies will form the foundation of my independent research career.